The anus is an evolutionary marvel

[nate_meurer]

I'm just as fascinated by the valve at the base of the stomach, called the pyloric sphincteric cylinder. It uses an ingenious mechanism to selectively pass liquid and very small particles to the small intestine, while keeping larger chunks in the stomach for further digestion. It functions like a screen or filter, but with a simple, robust, and reliable structure.

Here's a fantastic (and free) book about just this structure:

http://med.plig.org/

[drdeadringer]

> the pyloric sphincteric

Fun fact: I had pyloric stenosis as an infant. IIRC, this condition tends to hit first born males of which I am one.

Dearest mother kept bringing me into the hospital. "He keeps throwing up no matter what." She kept being told the "oh you're just a new mother" song until finally one doctor switched on a lightbulb to check something out.

Next thing is that I'm this infant on an adult stretcher being prep'd for surgery.

My oldest scar.

I swear if I was born 100 years earlier I'd be dead by starvation at no fault of anything but medical innovation.

[therealasdf]

I'm convinced that who ever came up with this valve was inspired by anuses. Its a clever way to dispense honey without making a mess.

Anus inspired honey dispenser https://imgur.com/a/jmQUSYr

[kccqzy]

To me the most fascinating aspect is not filtering out large chunks, but that it prevents the highly acidic gastric fluid (the pH ranges from 1 to 3) in the stomach from reaching and damaging the small intestine. The stomach is equipped to deal with the extremely acidic fluid for digestion, but the small intestine is not.

[barbarr]

>It uses an ingenious mechanism to selectively pass liquid and very small particles to the small intestine, while keeping larger chunks in the stomach for further digestion

Do you have an ELI5 for how this works?

[mrfusion]

So does it eventually give up and allow bigger objects through? You’d think it would need a mechanism to handle undigestible items (as any dog owner knows)

[bbkane]

This book is not super friendly to a newcomer to the sphinctor. I was unable to finish the Introduction due to the unexplained technical jargon immediately presented.

[gadders]

I can't hear talk of Pyloric Valves now without thinking of Confederacy of Dunces: https://en.wikipedia.org/wiki/A_Confederacy_of_Dunces (Great book btw)

[AceJohnny2]

My university CS department worked with a nearby hospital, and student projects were often related to medical imaging or modeling topics.

For a few years, there was work related to the anus, which according to the staff was an under-studied topic for obvious reasons.

I'm afraid I chickened out of choosing the "model the anal sphincter" project. In retrospect it sounded fun and interesting.

[sodapopcan]

The stuff about evolving the digestive tract to get more out of food is super interesting and never thought about it.

The whole thing about human buttocks as well I recently learned about after getting a dog of my own (ya ya, covid puppy acquirer here). I was always weirded out by my childhood dog's butt and read up on it while I was researching dog ownership before I got my current little buddy. I figured I was going to have to wipe his butt to ease my slight-yet-ever-present faecal phobia. I then learned that dogs (and most mammals) actually prolapse pretty extremely when pooping, making it so that poop rarely touches their butts (at least on short haired dogs). As it turns out, my pup's butt is generally the least smelly part of him!

Anyway, a bit of a ramble about a dog's butt that many probably already know, but(t) I found it fascinating.

[ervine]

"In hindsight it sounded fun and interesting."

[Tabular-Iceberg]

> Any live young who pass through the reproductive tract could also be imperiled by the proximity to poop-borne pathogens. Perhaps that’s why human anuses ventured off on their own.

Clearly not, since it's not really feasible to give birth without simultaneously defecating all over the place. One of more unpalatable secrets kept from men back in the era where you were supposed to just sit in a different room and smoke your cigar.

[3GuardLineups]

how...how do they manage that in the delivery room? They just throw away the bedding you're on after the delivery?

[throwaway-87b]

There was an old website 'anus' - the american nihilist underground society, and the essayist that ran it claimed his work would be complete when the anus was recognized to be as holy as the mouth.

Congratulations my man.

[therealasdf]

Im convinced that who ever came up with this valve was inspired by anuses. Its a clever way to dispense honey without making a mess.

Anus inspired honey dispenser https://imgur.com/a/jmQUSYr

[max_hammer]

Anus folding pattern are unique for every human being. So, they can be used as alternative to finger print.

[catblast01]

cf Smart Pipe https://youtu.be/DJklHwoYgBQ

[ectopod]

If your criminal activities leave anus prints you deserve to get caught.

[albrewer]

Someone just read your comment and got an idea for a startup.

[laylomo2]

Fun fact: Latin had long vowels as well as long consonants. So be careful with them or else you might be calling an old woman an anus.

ānus = ring / anus

annus = year

anus = old woman

[mikesabbagh]

my only problem is with hemorroids, what went wrong in the design there!!

[jandrese]

You gotta spend more hours each day chasing prey animals to exhaustion.

[markdown]

Evolution not keeping up with changes in diet I guess.

Do our primate cousins in the forests and zoos get hemorroids?

[dimovich]

Squating... The sitting toilets that we have now are not good for the body.

[adventured]

Another case of humans going against their evolutionary model.

[sneak]

We're all way past the evolutionary MTBF, thanks to antibiotics and vaccines. Not a lot of 20 year olds with that issue. This planet would have our current models dying of "natural causes" well before 35 if it weren't for our intentionally bucking the trend.

[bserge]

You're using it too much!

[gcapell]

If there was ever a time for the universal New Yorker caption: https://web.archive.org/web/20060203045552/http://modernarth... ...

[makeset]

"Christ, what an evolutionary marvel!"

[varyherb]

When I think about the digestive tract, I wonder—is the human body topologically equivalent to a torus?

[dsamarin]

It depends on the minimum size of the what you will consider a hole. Check out the video from VSauce on YouTube about how many holes a human has.

https://youtu.be/egEraZP9yXQ

[oh_sigh]

Specifically a g-holed torus, since the digestive tract isn't the only hole through the human body. At the very least, the mouth and ear are connected forming another hole.

[gadders]

Half of my comments start with "I heard a podcast the other day about this.." but I heard a podcast the other day that described how they had managed to get pigs to survive for multiple hours by inserting oxygenated liquid into their anus.

"Takanori - One is a very intuitive approach we just intubated, from the anus, just to provide oxygen gas continuously. This oxygen delivery is really able to persist survival in lethal conditions. Even up to 60 minutes or even longer.

Eva - 60 minutes of breathing through the rectum just by pumping in oxygen. Sounds amazing, but also like you could get a bit uncomfortable. The more clinically relevant approach uses a liquid that's very good at dissolving oxygen, perfluorocarbon or PFC. This liquid is already used by doctors during some ice surgeries and sometimes as a type of synthetic blood for transfusions. So we already know that it's safe for humans.

Takanori - So that liquid ventilation approach is also having greater impacts on oxygenation. So as to really rescue those fatal hypoxic conditions in the mouse, rats, and pig model system.

Eva - Incredibly, Takanori showed that when just less than a pint of this PFC was injected into the anus of pigs, they would stay happily oxygenated for up to 20 minutes when in respiratory failure. And they didn't stop there, by re-injecting every 20 minutes or so they could keep the pigs going for hours, or even more. Importantly though, when we breathe in and out using our lungs, we aren't just taking in oxygen. We're getting rid of carbon dioxide and other waste products too."

Transcript of interview: https://www.thenakedscientists.com/articles/interviews/intes...

NY Times article: https://www.nytimes.com/2021/05/14/science/rectum-breathing-...

//EDIT//Actual paper: https://www.cell.com/med/fulltext/S2666-6340(21)00153-7?utm_...

[Traubenfuchs]

Tell that to my hemorrhoids that make me cry -and what‘s with making it pleasurable to stick stuff inside this dirtiest part of our body???

Evolution sucks.

[beckerdo]

My friend once registered the domain "myan" in the top level domain "us". All sorts of adolescent hilarity ensued.

I see the domain is now available.

[antattack]

Thanks, now "you are an evolutionary marvel" sounds like an insult.

[samtuke]

Brilliant writing from the Atlantic.

[glaberficken]

Juvenile observation of the day: It's funny that this sits in the HN front page just above an article titled "Holes in the WiFi" :p

[haram_masala]

Not to be snarky, but isn’t every part of a successful organism an evolutionary marvel? If not, then perhaps a more interesting tale would be to look at the bodily systems that are substandard garbage. I’d probably start with the lower back.

[Turing_Machine]

The scrotum has all the marks of successive bad, hacky evolutionary patching.

Problem: Warm-bloodedness means the testicles are now too warm to work well.

Hack #1: Hang them on the outside of the body so they can stay cooler.

New problem resulting from first hack: Now they're much easier to damage.

Hack #2: Make them hurt really bad if they get bashed, so the owner takes great care to guard them.

The proper solution would have to make them more temperature-tolerant in the first place.

Interestingly, ovaries didn't go down this road, though there are certainly some suboptimal designs in that whole system as well.

[the_af]

> Not to be snarky, but isn’t every part of a successful organism an evolutionary marvel?

I prefer Stephen Jay Gould's point that lots of evolved subsystems are just kludges and jury-rigged solutions that just happen to work good enough, sort of. ("The Panda's Thumb").

[montenegrohugo]

Talk about an HN title.

[dang]

The second 'orifice' title in 24 hours, too. The previous thread ended up keeping itself together. Not sure about this one yet.

[mLuby]

Indeed. Not even a week since the last one:

Rectal Breathing with Perfluorocarbons (cell.com) https://news.ycombinator.com/item?id=27159001

[imoverclocked]

New title suggestions:

"Butts: finding the source."

or:

"Scientists Find That Hindsight is not 20/20"

[ekianjo]

Soon we will need a NSFW filter when browsing HN